1. Field of the Invention
The present invention relates to a close-up attachment lens to be attached to a photographic lens (main lens) of a camera on the object side, enabling close-up photography of a magnification from -0.5 to -1.0.
2. Description of the Related Art
Close-up attachment lenses, for example, which are disclosed in the laid-open Japanese Patent Publications (No.3-39917 and No.5-224121) have been known. In addition, the U.S. patent application Ser. No. (505,640), which was based on one of the Publications, JP3-39917, has been patented as the U.S. Pat. No. 5,216,546 (Jun. 1, 1993). Both of these laid-open patent publications and the U.S. patent have disclosed a three-lens-element arrangement, having two positive lens elements and one negative lens element.
However, as the magnification of the lens taught in the above laid-open Japanese Patent Publication No.3-39917 is -1.1 to -2.1, which is relatively high, the correction of spherical aberration and lateral chromatic aberration cannot sufficiently be made. On the other hand, the magnification of the lens taught in the above laid-open Japanese Patent Publication No.5-224121 is -0.9 to -0.80. This means that the magnification does not reach -1.0 (the life size), and is not suitable for the purposes of the close-up attachment lens of the present invention which has a magnification of -0.5 to -1.0. Furthermore, with the lens arrangement of JP5-224121, it should be noted that astigmatism and distortion are relatively large.
Generally, in order to satisfactorily correct aberrations, making the power of each lens weaker can be effective. However, if the power of the lenses are made too weak, the entire length the lens system becomes longer as well as the diameter of the lens on the object side increasing. Usually, in a main lens of a camera, there is a fixing member having thread groves for detachably attaching a filter or other accessories to the frontmost inner peripheral wall of the lens barrel of the main lens. However, if the lens diameter on the object side of the attachment lens is made larger, the internal diameter of an installing portion of the attachment lens inevitably becomes larger than the internal diameter of the fixing member of the main lens. Consequently, various sizes of accessories have to be prepared depending on the diameter on the object side of the attachment lens and that of the main lens.